Method of making synthetic resin articles such as teeth



v 13, 1949 v c, FEAGIN METHOD 0F MAKING SYN ETIC RESIN ARTICLES SUCH ABETH Filed Aug. 23, 1946 INVENTOR. a icz 5% flaw 1 W Patented Dec. 13,1949 METHOD OF'MAK ING sYN'iHETIoREsIN ARTICLES' SUCHAS TEETH Roy 0.Feagim-Flu'sh-ing, NnYi, 'assignor' to'iAus- :tenal Laboratories,lncorpor-ated New :York,

N. Y., a corporation-f New York Applica'tion August 23, 1946, SerialN05692i584 i'Claims. (Cl. 18-:55 .-1)

This invention relates, in general, to the :art of making plasticorsynthetic resin-like objects, and has particular relation to an improvedmethod of making teeth of plastic or synthetic res-inlike material. 5the problem iheretofore enoountered in' producing In'the.past,-variousmethods have been used molded plast-ic' aor syntheticresih like objects,formaking plastic orsynthetic resin-like teeth such as teeth, withoutlocalized shrink marks is andiotheiharticles of plastic or syntheticresineliminated; more partic'ularlwanimproved meth'-' like material. ingeneral, these methods are as odwith whichplastic or syntheticresin-liketeeth follows: may be producedwithout localized-shrink marks 1.Compression molding:.this' method uses two or' other.harmful'reifect-ontheappeaiahce or mold halves containing cavities into whichpowfunctioning of the teeth. der'is placed and-subsequently heated tomold- Anot r object of the invention is to accoming temperature. The twomold halves are then plish the new and advantageous res u set'fgfth.closed together by suitable pressure to procluce bygplacing between thedesired surface Of t e the molded article. uncured tooth body-andthe'adjacent surfaceof 2. Injection molding: according to this methodthe moldcavity a film of a' character to elimithe preheated plastic orsynthetic resin-like manate-shri'nkmarks on the surface of the toothterial is injected under pressure into the mold in ouring thesamaiandtouring the" plastic or cavity synthetic resin-like materialagainst this cumin 3. Transfer molding: in this method a plastic steadof curingit directlyagainst the: ac io or synthetic resin-like pre-formis heated outside the mold cavity. ofthe mold and then transferred tothe mold Another and more specific objectiof the invencavity, afterwhich'the mold halves are closed tiOD=ziS t0=flCCOIIlD1iSh the'new andadvantageous together by means of suitable pressure to form results setforth-in curing objects such asteeth the molded article. This method isused primarily formed of monomer-polymermat rial, for thermosettingmaterials. Another object-oftheinvention is to provide 4.Monomer-polymer molding: this method has a method ofmh described;having-the. been used in making dentures and artificial teeth, noveltyand advantages set forth, and charac and is carried out by mixingpolymerizable mate- 3() terizedby its simplicity and its economy andefrial ith itspolymer or other polymers to form fectivenessin use foraccomp'lishing the'desired a plastic dough. This dough is compressedinto results. a-mold cavity and is then cured under compres- Furtherobjects and advantages of the in'v'eii sion until the molded piece ishard or completely tion will appear from the following detailed decurecLscri-ption, takenin connection with the accom- In the use of monomericand polymeric methyl Denying drawing, in which the single figureis'niethacrylate, for example, the method has beena-vertical-sectionalviewof one illustrativ form carried out ordinarilyand in general by preof-toothmoldshowing'the'body of syntheticresinparing suitable plaster or plaster-like molds, like-material in themold cavity W h a fi1 pressing the dough mixture into these moldsaccording to'the present invention, between a'sur either for teeth,crowns, bridges, denture bases face of the body'of Syntheticres'in-likematerial or the like, closing the molds with pressure-and and theadjacentsurfaceof the mold cavity. placing them in water at suitablecuring tem- Referring now-tothe drawing, the reference: peratures. Witha monomer-polymer cure in e a l d 2 s g e, enerally, the two metal ms avery great difliculty has been nhalves respectiveiy'of a metal toothmold. The countered in producing molded plastic or synparticular'moldshown in the drawing is illusthetic resin-like objects,such as teeth,particutrative, and it is to be understood that the formlarlyv thosehaving considerable bulk, Without the andcharacter. of the mo d y Vary Wde y With-- molded objects containing localized shrink marks n th QD 0fp e e nvention. on the surface. These shrink marks produce in- The moldhalves 'l and 2 selected for illus accuracies and, in the case of teeth,produce teeth tration have cavity portions 3 and' l WhiCh, WheIl: whichdo not have a satisfactory appearance, themold isclosed,.define'a'cavity-forlfo mmgg' parti ularly where e localizedshrink arks 0 the 'desired- -plasticor synthetic resin-like object, curalong the labial surface of the tooth. Where suchuas artooth. The moldcavity shown in the the localized shrink marks are along the in-"drawing is awvnyromormmg anantenbrttotn-- :2 cisalor cusp area thetooth will notiunctioh correctly.

One ofithe'main-objects of the present inventionis toiplOVide animprovedmethod with which but this is also merely illustrative, it beingunderstood that the mold cavity may be of a configuration for forming aposterior tooth or other desired plastic or synthetic resin-like object.The mold halves I and 2 part along the dot and dash line aa, but thisalso may vary.

In making teeth according to the present invention of a plastic orsynthetic resin-like material comprising, for example, a.monomer-polymer material, the polymerizable material is mixed with itspolymer or other polymers to form a plastic dough. This dough is thenplaced in the mold cavity and between the mold halves l and 2 with afilm 5 between a surface or surfaces of the body 6 of themonomer-polymer material, and the adjacent surface or surfaces of themold cavity. The film 5 is shown between what is to form the labialsurface of the tooth made of the body 6 of monomer-polymer material andthe adjacent surface of the mold cavity. It may be placed between anyone or more of the surfaces of the uncured tooth body 6 and the adjacentsurface or surfaces of the mold cavity, for example, between one or moreof the labial, incisal or cusp surfaces of the tooth body and theadjacent surface or surfaces of the mold cavity.

The film 5 may be formed of plastic film material of suitable thickness,for example of the order of about .001 to .005", against the desiredsurface or surfaces of the tooth. The film material 5 is composed of anysuitable material which has the necessary strength and which can be madeto conform to the mold cavity. It is particularly desirable to use amaterial which contains no constituent which is reacted upon by theplastic or synthetic resin-like material used in making the teeth. Inother words, a plasticized film would not be as desirable for themanufacture of plastic or synthetic resin-like teeth as would anon-plasticized material, since the teeth have a tendency to extractsome of the plasticizer from the film and to produce a surface which isnot particularly desirable on a tooth. Such a surface is usually a fadedsurface and may have crow foot shrink marks thereon as well as lackingin vinyl chloride) cast film, a natural or synthetic rubber film, apolyvinyl alcohol film, polyethylene film, and a number of other filmmaterials are contemplated for securing the desired results.

Particularly I have found that a polyethylene; film is very satisfactoryfor this particular application with methyl methacrylate since thereisno solvent action of the methyl methacrylate on the film, and it is notsoftened even at curing temperatures of 100 C. It also has considerablegloss, and imparts this gloss to the tooth.

A natural rubber film has also been used to good advantage since it hasvery great strength and elasticity and conforms-very readily to verygreat depressions in the mold. This material is also not dissolved bymethyl methacrylate. The use of a synthetic rubber or rubber-like filmis also contemplated.

I have also used other polymerizable materials such as vinyl acetatemixed with methyl methacrylate polymer without having any effect uponthe film. This technique, therefore, will produce completelysatisfactory results on any monomerpolymer molding material, providedthe monomer portion has no solvent action on the film. Even if there isa slight solvent action, I still contemplate eliminating localizedshrink marks, and, since modifications in the resinous material of theteeth are contemplated, I do not intend to be restricted to the use of afilm against a methyl methacrylate composition alone, but with anypolymerizable mixture of monomers or polymers or other materials.

After placing the tooth material 6 in the mold cavity with the film 5 ofa character to eliminate shrink marks on the finished tooth or otherobject in place between the desired surface or surfaces of the uncuredbody 6 and the adjacent surface or surfaces of the mold cavity, the moldis closed with pressure and the body of plastic or synthetic resin-likematerial is cured, for example, by placing the mold in water at suitablecuring temperatures. As already described, with a film 5 ofpolyethylene, such film is not softened even at curing temperatures ofC.

Although I do not intend to be limited to the theory of the action whichtakes place, and reserve the right to correct or change the theory ifand when occasion requires, it seems that the use of a film 5 inaccordance with this invention and of the character described preventslocalized sticking of the body 6 of plastic or synthetic resin-likematerial to the surface of the mold cavity in curing the material andthereby localized shrink marks, fading of the color, or loss of gloss onthe tooth or other object. In other words, if shrinkage of the body 6occurs in ouring the same, it is uniform over the surface of the body 6,and thereby shrink marks, fading of color, and loss of the desiredglossy appearance are eliminated.

After curin of the tooth body 5 is completed, the mold is opened byseparating the mold parts I and 2 and the cured tooth is removed fromthe mold cavity. The film 5 may then be stripped or otherwise removedfrom the tooth or from the mold cavity if it tends in anywise to remainin the mold cavity.

An example of a suitable composition for the making of plastic teeth bythis method is as follows:

3 parts (by volume) methyl methacrylate polymer 1 part (by volume)methyl methacrylate monomer.

The material may be colored in both incisal and gingival shading, asdesired. These materials are then mixed carefully to a doughyconsistency, at which time they may be utilized in the pressing orinjection molding of the suitable incisal and gingival portions of thetooth.

The embodiment of the invention shown in the drawing is for illustrativepurposes only, and it is to be expressly understood that the drawing andthe accompanying specification are not to be construed as a definitionof the limits or scope of the invention, reference being bad to theappended claims for that purpose.

I claim:

1. A method of producing an article of polymerizable material whichcomprises: placing a film of polyethylene between a body of suchpolymerizable material and a forming surface having a contour to beimparted to the article, shaping the body of polymerizable material incontact with said film and to the contour of said surface,

and curing the polymerizable material while in contact with said film,said polymerizable material consisting essentially of an acryliccompound.

2. A method of producing an article of polymerizable material whichcomprises: placing a film of polyethylene between a body of suchpolymerizable material and a forming surface having a contour to beimparted to the article, shaping the body of polymerizable material incontact with said film and to the contour of said surface, and curingthe polymerizable material while in contact with said film, saidpolymerizable material consisting essentially of methyl methacrylatepolymer and methyl methacrylate monomer mixed to a doughy consistency.

3. A method of producing an artificial tooth of polymerizable materialwhich comprises: placing a film of polyethylene between a body of suchpolymerizable material and a forming surface having a contour to beimparted to the article, shaping the body of polymerizable material incontact with said film and to the contour of said surface, and curin thepolymerizable material while in contact with said film, saidpolymerizable material consisting essentially of methyl methacrylate.

4. A method of producing an article of polymerizable material whichcomprises: placin a REFERENCES CITED The following references are ofrecord in the file of this patent:

UNITED STATES PATENTS Number Name Date 2,067,580 Rohm Jan. 12, 1937FOREIGN PATENTS Number Country Date 484,343 Great Britain May 4, 1938

